Manufacturers are presently considering tin plated steel in the manufacture of gas tank containers for vehicles such as automobiles. The development of automotive tin coated gas tanks requires a coating for the exterior and interior of the containers. The exterior of the container must be protected from environmentally induced corrosion whereas the interior of the container must be resistant to corrosion induced by fuels contained therein. Additionally, the exterior coating must have a relatively hard surface. Although such a surface must be adaptive to welding and/or soldering additives, prior art coatings tended to decrease weldability.
The U.S. Pat. No. 4,391,855 to Geeck, issued Jul. 5, 1983, discloses resin coatings including cross linking agents. A secondary resin is added, such as melamine formaldehyde type cross linkers. Such linking agents required extended periods of time for cure as well as longer term baking or air drying. These resins were found to be too soft for exterior gas tank protection.
Gas tanks generally have lead and tin plate on their surface, as well as tin plated steel and zinc nickel electro-galvanized steel surfaces. Such surfaces are hard to coat, making adhesion of coatings to the surface a critical factor which must be considered in formulating a corrosion resistant coating. Although lower molecular weight resins disclosed in the prior art provide good adhesion to metal substrate and good formability, these resins result in coatings that are too soft for exterior gas tank protection. At the other extreme, higher molecular weight resins do not provide sufficient adhesion and do not provide sufficient formability.
The U.S. Pat. No. 4,748,194 to Geeck, discloses an improved protective coating for gas tank containers. This coating is well suited as a formulation for the exterior and interior of a gas tank. The invention utilized a specific mixture of linear epoxy and phenoxy resins to provide zinc rich coatings and charcoal zinc rich coatings for the exterior of the gas tank and aluminum coatings for the interior of the gas tank.
The present invention has been formulated for providing improved adhesion to new metals used in the gas tank art, such as tin plated steel. However, the present invention is further used as a coating on other metals, such as zinc and nickel combination on steel, hot dipped galvanizing and electro-galvanizing steel and cold rolled steel.